The present invention relates to a telemetry system for transmitting information detected by or relating to electronic devices such as implanted cardiac pacemakers or implanted medication dispensing devices to an external receiver for recording and analysis or for retransmission over phone lines to a remote location.
Adequate evaluation of the operation of implanted electronic prosthetic devices such as pacemakers is necessary to verify their proper operation and to avoid undetected premature performance degradation so that corrective steps may be taken promptly. Although some systems have been previously described which claim to have achieved adequate monitoring of one or more variables in connection with the operation of an implanted pacemaker, those systems have proven to be cumbersome in providing usable information to an external terminal.
In addition, the prior art systems have not generally attempted to solve the problems of transmitting information from a metal encased implantable device. Prior art systems have also failed to consider the compatibility of the telemetry system with a programmable pacemaker or other remotely programmed implantable device which operates at some times in response to an externally generated programming signal.
A telemetry patent, U.S. Pat. No. 4,026,305, to Tyers, relates to a telemetry system for transmitting a signal indicating the battery voltage of a pacemaker to an external monitor. The system disclosed in Tyers is not usable for transmission of electrocardiogram information or for digital data. The Tyers system uses a low pass system which includes 60 Hz and 120 Hz.
Further, the problem of minimizing the power consumption of a two-way telemetry system capable of transmission through a metal shield has not been adequately addressed.
The present invention accordingly provides a two-way telemetry system utilizing an improved ultra-low power circuit for transmission of pacemaker EKG, analog data, or stored digital data to an external terminal. The system operates to permit monitoring of the electrical activity on the lead of an implantable pacemaker without attaching external or catheter electrodes to the patient. The receiver uses a bandpass system which operates above the common noise frequencies of 60 Hz and 120 Hz.
To receive transmitted data, a receiving coil antenna is placed over the implantable pacemaker and the pacemaker is commanded by applying a programming signal to its circuitry to cause it to send out the electrogram, the pacing pulse, or other data to the remote receiver.
The transmitting circuitry of the present invention is compatible with the antenna and receiving circuitry shown in co-pending application entitled Digital Cardiac Pacemaker, filed Nov. 6, 1978, under Ser. No. 957,958, now U.S. Pat. No. 4,230,128 naming Ray S. McDonald as the inventor. That application discloses a pacemaker pulse generator which can be remotely programmed.